Electronic apparatus

ABSTRACT

An electronic component generates heat in an electronic apparatus. The heat of the electronic component is transferred to a thermal conductive plate of a heat receiver in a liquid cooling unit. The heat is transferred to coolant from the thermal conductive plate. The temperature of the coolant rises. The heat exchanger absorbs heat of the coolant. The coolant gets cooled. The heat of the electronic component is also transferred to the printed wiring board. The heat spreads over the printed wiring board through a wiring pattern in the printed wiring board. Since the tank or/and pump is placed at a position outside the printed wiring board, the heat cannot be transferred to the tank or/and the pump. This results in prevention of rise in the temperature of the coolant in the tank or/and the pump. The efficiency of heat radiation can thus be enhanced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic apparatus such as anotebook personal computer, for example.

2. Description of the Prior Art

A printed wiring board is incorporated in an electronic apparatus. Anelectronic component such as a large-scale integrated circuit (LSI) chipis mounted on the printed wiring board. A liquid cooling unit is placedon the printed wiring board so as to cool the electronic component. Theliquid cooling unit includes a closed circulating loop for coolant. Aheat receiver such as a liquid cooling jacket is inserted in the closedcirculating loop. The heat receiver is received on the electroniccomponent. A pump and a tank are inserted in the closed circulatingloop. The pump and the tank are placed on the printed wiring board.

The electronic component generates heat during operation. The heat ofthe electronic component is transferred to the heat receiver and theprinted wiring board. The temperature of the printed wiring board thusrises. Since the pump and the tank are located on the printed wiringboard, the rise in the temperature of the printed wiring board leads torise in the temperature of the coolant in the pump and the tank. Theheat cannot thus sufficiently be transferred from the electroniccomponent to the coolant.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide anelectronic apparatus allowing an enhanced efficiency of heat radiation.

According to a first aspect of the present invention, there is providedan electronic apparatus comprising: a printed wiring board; anelectronic component mounted on the printed wiring board; a closedcirculating loop; a heat receiver inserted in the closed circulatingloop, the heat receiver having a thermal conductive plate received onthe electronic component, the heat receiver defining a flow passage onthe thermal conductive plate; a heat exchanger inserted in the closedcirculating loop so as to absorb heat from coolant; and a tank insertedin the closed circulating loop at a position outside the printed wiringboard so as to store air in the closed circulating loop.

The electronic component generates heat in the electronic apparatus. Theheat of the electronic component is transferred to the thermalconductive plate of the heat receiver. The heat is transferred tocoolant from the thermal conductive plate. The temperature of thecoolant thus rises. The heat exchanger absorbs the heat of the coolant.The coolant gets cooled. The heat of the electronic component is alsotransferred to the printed wiring board. The heat spreads over theprinted wiring board through a wiring pattern in the printed wiringboard. Since the tank is placed at a position outside the printed wiringboard, the heat cannot be transferred to the tank. This results inprevention of rise in the temperature of the coolant in the tank. Theefficiency of heat radiation can thus be enhanced.

The electronic apparatus may further comprise a pump inserted in theclosed circulating loop at a position outside the printed wiring boardso as to circulate the coolant along the closed circulating loop. Aslong as the pump is placed at a position outside the printed wiringboard, the heat generated in the printed wiring board cannot betransferred to the pump. This results in prevention of rise in thetemperature of the coolant in the pump. The efficiency of heat radiationcan thus be further enhanced. A partition plate may be placed in a spacebetween the tank and the printed wiring board. The partition plateserves to prevent air having the heat of the electronic component fromrunning toward the tank. This results in prevention of rise in thetemperature of the coolant in the tank.

According to a second aspect of the present invention, there is providedan electronic apparatus comprising: a printed wiring board; anelectronic component mounted on the printed wiring board; a closedcirculating loop; a heat receiver inserted in the closed circulatingloop, the heat receiver having a thermal conductive plate received onthe electronic component, the heat receiver defining a flow passage onthe thermal conductive plate; a heat exchanger inserted in the closedcirculating loop so as to absorb heat from coolant; and a pump insertedin the closed circulating loop at a position outside the printed wiringboard so as to circulate the coolant along the closed circulating loop.The heat generated in the printed wiring board cannot be transferred tothe pump in the same manner as described above. This results inprevention of rise in the temperature of the coolant in the pump. Theefficiency of heat radiation can be further enhanced. A partition platemay be placed in a space between the pump and the printed wiring board.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following description of thepreferred embodiments in conjunction with the accompanying drawings,wherein:

FIG. 1 is a perspective view schematically illustrating a notebookpersonal computer as a specific example of an electronic apparatusaccording to a first embodiment of the present invention;

FIG. 2 is a perspective view schematically illustrating the innerstructure of the notebook personal computer;

FIG. 3 is a plan view schematically illustrating a liquid cooling unitaccording to a specific embodiment of the present invention;

FIG. 4 is a sectional view schematically illustrating a heat receiveraccording to a specific example of the present invention;

FIG. 5 is a sectional view taken along the line 5-5 in FIG. 4;

FIG. 6 is a partial sectional view schematically illustrating a fanunit;

FIG. 7 is a sectional view taken along the line 7-7 in FIG. 6, forschematically illustrating a heat exchanger according to a specificexample of the present invention;

FIG. 8 is a sectional view taken along the line 8-8 in FIG. 7;

FIG. 9 is a front schematic view of an inflow nozzle;

FIG. 10 is a sectional view, corresponding to FIG. 7, schematicallyillustrating a heat exchanger according to another specific example ofthe present invention;

FIG. 11 is a sectional view, corresponding to FIG. 7, schematicallyillustrating a heat exchanger according to still another specificexample of the present invention;

FIG. 12 is a sectional view, corresponding to FIG. 8, schematicallyillustrating a heat exchanger according to still another specificexample of the present invention;

FIG. 13 is a sectional view, corresponding to FIG. 8, schematicallyillustrating a heat exchanger according to still another specificexample of the present invention;

FIG. 14 is a perspective view schematically illustrating the innerstructure of a notebook personal computer according to a secondembodiment of the present invention;

FIG. 15 is a perspective view schematically illustrating a main bodyenclosure;

FIG. 16 is a sectional view, corresponding to FIG. 4, schematicallyillustrating a heat receiver according to a specific example of thepresent invention;

FIG. 17 is a sectional view taken along the line 17-17 in FIG. 16;

FIG. 18 is a sectional view, corresponding to FIG. 8, schematicallyillustrating a heat exchanger according to still another specificexample of the present invention; and

FIG. 19 is a sectional view, corresponding to FIG. 8, schematicallyillustrating a heat exchanger according to still another specificexample of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates a notebook personal computer 11 as aspecific example of an electronic apparatus according to a firstembodiment of the present invention. The notebook personal computer 11includes a thin first enclosure, namely a main body enclosure 12, and asecond enclosure, namely a display enclosure 13. The display enclosure13 is coupled to the main body enclosure 12 for relative swingingmovement. The main body enclosure 12 includes a base 12 a and a cover 12b removably coupled to the base 12 a. Input devices such as a keyboard14 and a pointing device 15 are embedded in the surface of the cover 12b, for example. Users manipulate the keyboard 14 and/or the pointingdevice 15 to input commands and/or data.

A liquid crystal display (LCD) panel module 16 is enclosed in thedisplay enclosure 13, for example. The screen of the LCD panel module 16exposes within a window opening 17 defined in the display enclosure 13.Texts and graphics appear on the screen. Users can see the ongoingoperation of the notebook personal computer 11 based on the texts andgraphics on the screen. The display enclosure 13 can be superposed onthe main body enclosure 12 through the swinging movement relative to themain body enclosure 12.

As shown in FIG. 2, a printed circuit board unit 18 is placed in theinner space defined in the main body enclosure 12. The printed circuitboard unit 18 includes a printed wiring board 19 and electroniccomponents, namely first and second large-scale integrated circuit (LSI)packages 21, 22, mounted on the surface of the printed wiring board. Thefirst LSI package 21 includes a central processing unit (CPU) chip, notshown, mounted on a small-sized substrate, for example. The second LSIpackage includes a video chip, not shown, mounted on a small-sizedsubstrate, for example. The CPU chip is designed to execute variouskinds of processing based on an operating system (OS) and/or applicationsoftware, for example. The video chip is designed to execute imageprocessing based on the processing of the CPU chip, for example.

Storage medium drives or storage devices, such as digital versatile disk(DVD) drive 23 and a hard disk drive, HDD, 24, are placed in the innerspace of the main body enclosure 12 at a position outside the printedwiring board 19. The aforementioned operating system and applicationsoftware may be stored in the hard disk drive 24. A card unit 25 isplaced in the inner space of the main body enclosure 12. PC cards, suchas a memory card, a small computer system interface (SCSI) card and alocal area network (LAN) card, are inserted into the card unit 25through the card slot. The card unit 25 may be mounted on the printedwiring board 19, for example.

A liquid cooling unit 27 is placed on the printed wiring board 19 in theinner space of the main body enclosure 12. The liquid cooling unit 27includes a first heat receiver 28 received on the first LSI package 21.The first heat receiver 28 is designed to absorb heat generated in theCPU chip. Screws may be utilized to fix the first heat receiver 28 ontothe printed wiring board 19, for example. The liquid cooling unit 27allows establishment of a closed circulating loop for coolant. The firstheat receiver 28 is inserted in the closed circulating loop. Here,antifreeze of propylene glycol series may be utilized as coolant, forexample. The first heat receiver 28 will be described later in detail.

A second heat receiver 29 is inserted in the closed circulating loop.The second heat receiver 29 is received on the second LSI package 22.The second heat receiver 29 is located at a position downstream of thefirst heat receiver 28. The second heat receiver 29 includes a thermalconductive plate received on the video chip. The second heat receiver 29absorbs heat from the video chip in this manner. The thermal conductiveplate is coupled to a metallic tube, which will be described later.Screws may be utilized to fix the thermal conductive plate onto theprinted wiring board 19, for example. The thermal conductive plate maybe made of a metallic material having thermal conductivity, such asaluminum, for example.

A heat exchanger 31 is inserted in the closed circulating loop so as toabsorb heat from coolant. The heat exchanger 31 is located at a positiondownstream of the second heat receiver 29. The heat exchanger 31 isopposed to a ventilation opening defined in a fan unit 32. Screws may beutilized to fix the heat exchanger 31 and the fan unit 32 onto theprinted wiring board 19, for example. The heat exchanger 31 is placedbetween the fan unit 32 and an air outlet 33 defined in the main bodyenclosure 12. The fan unit 32 generates airflow sequentially runningthrough the heat exchanger 31 and the air outlet 33. The heat exchanger31 and the fan unit 32 will be described later in detail. The fan unit32 may be placed within a recess formed in the printed wiring board 19.

The fan unit 32 includes a fan housing 34. The fan housing 34 defines apredetermined inner space. The air inlet 35 is formed in each of the topand bottom plates of the fan housing 34. The air inlets 35 spatiallyconnect the inner space of the fan housing 34 to a space outside the fanhousing 34. A fan 36 is placed in the inner space of the fan housing 34.

A tank 37 is inserted in the closed circulating loop. The tank 37 islocated at a position downstream of the heat exchanger 31. The tank 37may be made of a metallic material having thermal conductivity such asaluminum, for example. Screws may be utilized to fix the tank 37 ontothe printed wiring board 19, for example. The tank 37 serves to storethe coolant and air in the closed circulating loop. The coolant and airare kept in a storage space defined in the tank 37. A coolant outlet isdefined in the storage space. The coolant outlet is set at a positionclosest to the bottom of the storage space. Even if the coolant isleaked out of the circulating loop because of evaporation, for example,the gravity makes the coolant kept on the bottom of the storage space.Only the coolant is allowed to flow into the coolant outlet, so that airis prevented from reaching an outlet nozzle, which will be describedlater in detail.

A pump 38 is inserted in the closed circulating loop. The pump 38 islocated at a position downstream of the tank 37. The first heat receiver28 is located at a position downstream of the pump 38. Screws may beutilized to fix the pump 38 onto the printed wiring board 19. Apiezoelectric pump may be utilized as the pump 38, for example. Apiezoelectric element is incorporated in the piezoelectric pump. Whenthe piezoelectric element vibrates in response to supply of electricpower, the coolant is discharged from the pump 38 to the first heatreceiver 28. The pump 38 allows the circulation of the coolant throughthe closed circulating loop in this manner. The pump 38 may be made of aresin material having a relatively low liquid permeability, such aspolyphenylene sulfide (PPS), for example. Alternatively, a cascade pump,a piston pump, or the like, may be utilized as the pump 38, for example.

As shown in FIG. 3, a tube 41 is utilized for each connection betweenthe first heat receiver 28 and the second heat receiver 29, between thesecond heat receiver 29 and the heat exchanger 31, between the heatexchanger 31 and the tank 37, between the tank 37 and the pump 38, andbetween the pump 38 and the first heat receiver 28. The ends of thetubes 41 are coupled to metallic tubes 42 attached to the first heatreceiver 28, the second heat receiver 29, the heat exchanger 31, thetank 37 and the pump 38, respectively. Fixing members, not shown, suchas bands, may be utilized to fix the tubes 41 onto the correspondingmetallic tubes 42.

The tubes 41 may be made of an elastic resin material havingflexibility, such as rubber, for example. The metallic tubes 42 may bemade of a metallic material having thermal conductivity, such asaluminum, for example. The elasticity of the tubes 41 serves to absorbrelative positional shifts between the first heat receiver 28, thesecond heat receiver 29, the heat exchanger 31, the tank 37 and the pump38. The length of the respective tubes 41 may be set minimum enough toaccept the relative positional shifts. Decoupling of the tubes 41 fromthe corresponding metallic tubes 42 allows independent replacement ofthe first heat receiver 28, the second heat receiver 29, the heatexchanger 31, the tank 37 and the pump 38 in a relatively facilitatedmanner.

As shown in FIG. 4, the first heat receiver 28 includes a box-shapedcasing 44, for example. The casing 44 defines a closed inner space. Thecasing 44 may be made of a metallic material having thermalconductivity, such as aluminum, for example. The casing 44 includes abottom plate defining a flat thermal conductive plate 45. A flow passage46 is defined on the thermal conductive plate 45.

At least two inflow nozzles 47, 47 are coupled to the casing 44 atpositions outside the periphery of the thermal conductive plate 45 so asto extend into the casing 44 from the outside. The inflow nozzles 47, 47have discharge openings opposed to the upstream end of the flow passage46. The inflow nozzles 47 may be formed in a cylindrical shape, forexample. The inflow nozzles 47 may bifurcate from the metallic tube 42.The inflow nozzles 47, 47 are placed to extend along parallel lines. Inthis case, the inflow nozzles 47, 47 may be set in parallel with eachother. The flow passage 46 is designed to extend on the extensions ofthe inflow nozzles 47.

An outflow nozzle 48 is coupled to the casing 44 at a position outsidethe periphery of the thermal conductive plate 45. The outflow nozzle 48has an inflow opening opposed to the downstream end of the flow passage46. The outflow nozzle 48 may be formed in a cylindrical shape, forexample. The inflow nozzles 47 and the outflow nozzle 48 are oriented inthe same direction. When the coolant flows into the flow passage 46 fromthe inflow nozzles 47, the coolant flows along the inner surface of thecasing 44. The inner surface of the casing 44 allows the coolant to turnaround. The coolant thus flows to the outflow nozzle 48 along the innersurface of the casing 44. The coolant is discharged from the outflownozzle 48. The coolant absorbs heat from the thermal conductive plate45. The flow passage 46 takes a U-shape in the casing 44 in this manner.

Heat radiating fins 49 are arranged on the thermal conductive plate 45in a zigzag pattern. The heat radiating fins 49 stand upright from thesurface of the thermal conductive plate 45. The heat radiating fins 49are designed to extend in the direction of the coolant flow. The heatradiating fins 49 may be made of a metallic material having thermalconductivity, such as aluminum, for example. The heat radiating fins 49may be formed integral with the thermal conductive plate 45, forexample. Since the heat radiating fins 49 are arranged in a zigzagpattern, the aforementioned flow passage 46 is kept between the heatradiating fins 49 in the direction of the coolant flow. The coolant canflow through the flow passage 46 without stagnating. Heat is transmittedto the heat radiating fins 49 from the thermal conductive plate 45. Thecoolant absorbs the heat from the heat radiating fins 49.

As shown in FIG. 5, the thermal conductive plate 45 is received on a CPUchip 51 in the first LSI package 21. The first LSI package 21 may beformed as a pin grid array (PGA) package. The first LSI package 21 maybe received on a socket mounted on the printed wiring board 19, forexample. A heat spreader 52 in the shape of a plate is interposedbetween the CPU chip 51 and the thermal conductive plate 45. The heatspreader 52 may be made of a metallic material having a high thermalconductivity, such as copper, for example. The heat spreader 52 servesto transfer heat of the CPU chip 51 to the thermal conductive plate 45in an efficient manner.

The casing 44 includes a depression 53 sinking from the thermalconductive plate 45 between the downstream end of the flow passage 46and the outflow nozzle 48. The depression 53 provides a space 54 havingthe level lower than the flow passage 46 in the casing 44. The outflownozzle 48 is designed to extend into the space 54. The inflow opening ofthe outflow nozzle 48 is thus opposed to the peripheral edge of thethermal conductive plate 45. The casing 44 likewise defines a depression53 a sinking from the thermal conductive plate 45 between the upstreamend of the flow passage 46 and the inflow nozzles 47, 47. The depression53 a provides a space 54 a having the level lower than the flow passage46 in the casing 44. The inflow nozzles 47, 47 are designed to extendinto the space 54 a. The openings of the inflow nozzles 47 are in thismanner opposed to the peripheral edge of the thermal conductive plate45. The casing 44 also defines a top plate 55. The top plate 55 isopposed to the thermal conductive plate 45 and the depressions 53, 53 a.

The first heat receiver 28 allows establishment of the depressions 53,53 a between the downstream end of the flow passage 46 and the outflownozzle 48 as well as between the upstream end of the flow passage 46 andthe inflow nozzles 47, respectively. Specifically, the spaces 54, 54 aare positioned outside the periphery of the thermal conductive plate 45,namely the first LSI package 21. The outflow and inflow nozzles 48, 47are designed to extend into the spaces 54, 54 a, respectively. Thecasing 44 is thus prevented from an increase in the thickness of thecasing 44 as compared with the case where the inflow and outflow nozzles47, 48 extends in the flow passage 46 inside the periphery of the firstLSI package 21. This results in reduction in the height of the firstheat receiver 28 from the front surface of the printed wiring board 19.The first heat receiver 28 having a reduced height significantlycontributes to reduction in the thickness of the main body enclosure 12.

The thermal conductive plate 45 extends in the horizontal direction inthe casing 44. Since the space 54 sinks from the flow passage 46, thegravity forces the coolant to flow into the space 54 from the flowpassage 46. Even if the coolant is leaked out of the closed circulatingloop because of evaporation from the tubes 41, the pump 38, and thelike, for example, the coolant can constantly be maintained in the space54. Even if air gets into the flow passage 46, the air goes up towardthe top plate 55 in the space 54. The outflow nozzle 48 is thusprevented from sucking air as much as possible. This results inprevention of circulation of the air through the closed circulatingloop.

As shown in FIG. 6, the fan 36 has the structure of a so-calledcentrifugal fan. The fan 36 includes a rotating body 56 and blades 57extending outward in the radial directions from the rotating body 56.When the fan 36 is driven for rotation around a rotation axis 58, freshair is introduced along the rotation axis 58 through the air inlets 35,35 of the bottom and top plates of the fan housing 34. The rotation ofthe fan 36 serves to generate airflow running in the centrifugaldirection.

A ventilation opening 59 is defined in the fan housing 34 at a positionoutside the orbit of the blades 57. The heat exchanger 31 is placedbetween the ventilation opening 59 and the air outlet 33. Thecentrifugal airflow is guided to the ventilation opening 59 along theinner surface of the fan housing 34. The air is discharged from theventilation opening 59 in this manner. The discharged air sequentiallyruns through the heat exchanger 31 and the air outlet 33. The heatexchanger 31 is designed to extend in the direction perpendicular to thedirection of the airflow.

As shown in FIG. 7, the heat exchanger 31 includes a first flat plate 61extending in parallel with the bottom surface of the base 12 a. A secondflat plate 62 is opposed to the front surface of the first flat plate61. The second flat plate 62 extends in parallel with the first flatplate 61. The peripheral edges of the first and second flat plates 61,62 are coupled to each other. A flat space 63 is in this manner definedbetween the first and second flat plates 61, 62 along the front surfaceof the first flat plate 61. The flat space 62 serves as a flow passage.The flat space 63 is designed to extend along an imaginary planeincluding the longitudinal axis of the metallic tube 42. The first andsecond flat plates 61, 62 are made of a metallic material having thermalconductivity, such as aluminum, for example.

First heat radiating fins 64 are formed to stand upright from the outersurface of the first flat plate 61. Second heat radiating fins 65 arelikewise formed to stand upright from the outer surface of the secondflat plate 62. The first and second heat radiating fins 64, 65 aredesigned to extend from the ventilation opening 59 of the fan unit 32 tothe air outlet 33. Airflow passages are defined between the adjacentfirst heat radiating fins 64, 64 and between the adjacent second heatradiating fins 65, 65. The airflow runs through the airflow passagesalong the outer surfaces of the first and second flat plates 61, 62. Thefirst and second heat radiating fins 64, 65 are made of a metallicmaterial having thermal conductivity, such as aluminum, for example.

As shown in FIG. 8, the flat space 63 extends wide in the horizontaldirection. The flat space 63 thus provides a flow passage having asufficiently large cross-section as compared with the cross-section ofthe metallic tube 42. The flow speed of the coolant is suppressed at theflat space 63. The coolant is allowed to flow through the flat space 63at a relatively low speed in this manner. The coolant thus contacts thefirst and second flat plates 61, 62 for a relatively longer time. Theheat of the coolant can sufficiently be transferred to the first andsecond flat plates 61, 62. The airflow can absorb the heat of thecoolant in an efficient manner.

Now, assume that the coolant circulates along the closed circulatingloop. Antifreeze of propylene glycol series, for example, is utilized asthe coolant as described above. When the notebook personal computer 11is switched on, the CPU chip 51 starts the operation of the fan unit 32.The fan 36 is driven for rotation. Fresh air is introduced through anair inlet, not shown, formed in the main body enclosure 12. The air isintroduced along the rotation axis 58 through the air inlets 35. Theairflow thus runs along the front and back surfaces of the printedwiring board 19. Simultaneously, the CPU chip 51 directs the operationof the pump 38. The circulation of the coolant is thus generated in theclosed circulating loop.

The CPU chip 51 generates heat of a first calorific power or a higherthermal energy during the operation of the CPU chip 51. The heat of theCPU chip 51 is transferred to the thermal conductive plate 45 and theheat radiating fins 49 of the first heat receiver 28. The coolant in theflow passage 46 absorbs the heat of the thermal conductive plate 45 andthe heat radiating fins 49. The coolant flows into the flow passage 46through the inflow nozzles 47, 47. Two streams of the coolant aregenerated in the flow passage 46 in this manner. The streams expand inthe horizontal direction in the flow passage 46. The coolant flowsthrough the flow passage 46 without stagnating. The coolant can absorbthe heat of the thermal conductive plate 45 in an efficient manner. TheCPU chip 51 gets cooled in this manner.

The coolant flows from the first heat receiver 28 to the second heatreceiver 29. The video chip generates heat of a second calorific powersmaller than the first calorific power, namely a lower thermal energy,during the operation of the video chip. The heat of the video chip istransferred to the thermal conductive plate of the second heat receiver29. The coolant in the metallic tube 42 absorbs the heat of the thermalconductive plate. The video chip gets cooled in this manner. The coolantflows into the heat exchanger 31 from the second heat receiver 29. Inthis case, the video chip generates heat of the second calorific powersmaller than the first calorific power of heat generated at the CPU chip51. The coolant is first subjected to cooling action of the CPU chip 51having a larger thermal energy. The CPU chip 51 and the video chip canthus be cooled in an efficient manner.

The coolant flows into the flat space 63 in the heat exchanger 31. Theheat of the coolant is transferred to the first and second flat plates61, 62 as well as the first and second heat radiating fins 64, 65. Thefan unit 32 generates airflow from the ventilation opening 59 to the airoutlet 33. The heat of the coolant is radiated into the air from theouter surfaces of the first and second flat plates 61, 62 and thesurfaces of the first and second heat radiating fins 64, 65. The coolantthus gets cooled. The air is discharged out of the main body enclosure12 through the air outlet 33. The coolant flows into the tank 37. Thecoolant then flows into the pump 38 from the tank 37.

The liquid cooling unit 27 of the notebook personal computer 11 isplaced within the inner space of the main body enclosure 12. Nocomponent of the liquid cooling unit 27 is incorporated in the displayenclosure 13. Accordingly, no tube 41 and no metallic tube 42 extendbetween the main body enclosure 12 and the display enclosure 13. Theliquid cooling unit 27 can be assembled into the main body enclosure 12in a relatively facilitated manner in the process of making the notebookpersonal computer 11. This results in reduction in the cost of makingthe notebook personal computer 11. The liquid cooling unit 27 is alsoremoved from the main body enclosure 12 in a relatively facilitatedmanner.

In addition, when the notebook personal computer 11 is placed on thedesk, the main body enclosure 12 is set on the desk, for example. As isapparent from FIG. 1, the main body enclosure 12 takes the horizontalattitude. The display enclosure 13 takes an inclined attitude around theedge of the main body enclosure 12. Since the liquid cooling unit 27 isincorporated in the main body enclosure 12, the weight of the liquidcooling unit 27 serves to locate the centroid of the notebook personalcomputer 11 at a lower position. The notebook personal computer 11 isthus allowed to enjoy a stabilized attitude.

In addition, the first heat receiver 28, the second heat receiver 29,the heat exchanger 31, the tank 37 and the metallic tubes 42 are allmade of aluminum in the liquid cooling unit 27. The coolant is thusprevented from contacting with any metallic material other than aluminumin the closed circulating loop. The coolant is prevented from sufferingfrom elution of metallic ions. This results in prevention of corrosionof the first heat receiver 28, the second heat receiver 29, the heatexchanger 31, the tank 37 and the metallic tubes 42. The coolant is inthis manner prevented from leakage from the closed circulating loop.

In addition, the first and second flat plates 61, 62 of the heatexchanger 31 are allowed to contact with the first and second heatradiating fins 64, 65 at larger areas as compared with the case where acylindrical tube is utilized to define the flow passage. This results inan enhanced efficiency of heat radiation. Moreover, the flat space 63 isdesigned to expand along an imaginary plane including the longitudinalaxis of the metallic tube 42. Even when the coolant flows in a reducedamount, the coolant is allowed to contact the first and second flatplates 61, 62 over a larger area. This results in a further enhancedefficiency of heat radiation.

As shown in FIG. 9, the tip ends of the inflow nozzles 47 may expand inthe horizontal or lateral direction in the first heat receiver 28, forexample. In this case, the tip ends of the inflow nozzles 47 may expandin a direction parallel to the thermal conductive plate 45 and the topplate 55. The inflow nozzles 47 allow the coolant to expand in thehorizontal direction in the flow passage 46 through the tip ends of theinflow nozzles 47. The stream of the coolant is allowed to furtherexpand in the horizontal direction in the flow passage 46. The coolantabsorbs heat from the thermal conductive plate 45 and the heat radiatingfins 49 in a highly efficient manner.

As shown in FIG. 10, the liquid cooling unit 27 may include a heatexchanger 31 a in place of the aforementioned heat exchanger 31. Theheat exchanger 31 a includes third and fourth flat plates 66, 67 inaddition to the aforementioned first and second flat plates 61, 62. Thethird flat plate 66 is opposed to the front surface of the second flatplate 62. The fourth flat plate 67 is opposed to the front surface ofthe third flat plate 66. The peripheral edges of the third and fourthflat plates 66, 67 are coupled to each other. A flat space 68 is definedbetween the third and fourth flat plates 66, 67 along the front surfaceof the third flat plate 66 in this manner. The flat space 68 serves as aflow passage. The third and fourth flat plates 66, 67 are made of ametallic material having thermal conductivity, such as aluminum, forexample.

The first heat radiating fins 64 are formed to stand upright from theouter surface of the first flat plate 61 in the same manner as theaforementioned heat exchanger 31. The second heat radiating fins 65 arelikewise formed to stand upright from the outer surface of the fourthflat plate 67. A gap is defined between the front surface of the secondflat plate 62 and the back surface of the third flat plate 66 in thismanner. This gap serves as an airflow passage extending from theventilation opening 59 of the fan unit 32 to the air outlet 33.

Support columns 69, 69 are placed in the gap between the front surfaceof the second flat plate 62 and the back surface of the third flat plate66. The support columns 69 are interposed between the second and thirdflat plates 62, 66. The support columns 69 serve to maintain the gapbetween the second and third flat plates 62, 66. Even when an urgingforce is applied to the first and second flat plates 61, 62 toward thethird and fourth flat plates 66, 67, or even when an urging force isapplied to the third and fourth flat plates 66, 67 toward the first andsecond flat plates 61, 62, during the process of making the heatexchanger 31 a, the first to fourth flat plates 61, 62, 66, 67 isreliably prevented from deformation. This results in prevention ofreduction in the cross-section of the gap between the second flat plate62 and the third flat plate 66.

The heat exchanger 31 a allows establishment of the parallel flat spaces63, 68. The coolant flows through the flat spaces 63, 68. Thecross-section of the flow passage can be increased as compared with theaforementioned heat exchanger 31. This results in a reduction in theflow speed of the coolant. The coolant is allowed to flow through theflat spaces 63, 68 at a lower speed. The coolant contacts with the firstand second flat plates 61, 62 and the third and fourth flat plates 66,67 for a longer time. The heat of the coolant can thus sufficiently betransferred to the first and second flat plates 61, 62 and the third andfourth flat plates 66, 67. The airflow absorbs the heat from the coolantin an efficient manner.

Moreover, the airflow runs through the gap defined between the secondand third flat plates 62, 66. The airflow runs along the front surfaceof the second flat plate 62 and the back surface of the third flat plate66. The heat is radiated into the air from the front surface of thesecond flat plate 62 and the back surface of the third flat plate 66.This results in an enhanced efficiency of heat radiation as comparedwith the aforementioned heat exchanger 31.

As shown in FIG. 11, the liquid cooling unit 27 may include a heatexchanger 31 b in place of the aforementioned heat exchangers 31, 31 a.The heat exchanger 31 b includes fifth and sixth flat plates 71, 72 inaddition to the first and second flat plates 61, 62 and the third andfourth flat plates 66, 67 of the heat exchanger 31 a. The fifth flatplate 71 is opposed to the front surface of the second flat plate 62.The sixth flat plate 72 is opposed to the front surface of the fifthflat plate 71. The sixth flat plate 72 is also opposed to the backsurface of the third flat plate 66. The peripheral edges of the fifthand sixth flat plates 71, 72 are coupled to each other. A flat space 73is defined between the fifth and sixth flat plates 71, 72 along thefront surface of the fifth flat plate 71. The flat space 73 serves as aflow passage. The fifth and sixth flat plates 71, 72 are made of ametallic material having thermal conductivity, such as aluminum, forexample.

The first heat radiating fins 64 are formed to stand upright from theouter surface of the first flat plate 61 in the same manner as theaforementioned heat exchanger 31 a. The second heat radiating fins 65are formed to stand upright from the outer surface of the fourth flatplate 67. A gap is defined between the front surface of the second flatplate 62 and the back surface of the fifth flat plate 71. A gap is alsodefined between the front surface of the sixth flat plate 72 and theback surface of the third flat plate 66. These gaps serve as airflowpassages extending from the ventilation opening 59 of the fan unit 32 tothe air outlet 33. The support columns 69, 69 may be placed in each ofthe gaps in the same manner as described above.

Three of the flat spaces 63, 68, 73 are defined along parallel lines inthe heat exchanger 31 b. The coolant flows through the flat spaces 63,68, 73. The cross-section of the flow passage is increased as comparedwith the aforementioned heat exchangers 31, 31 a. The coolant is allowedto flow through the flat spaces 63, 68, 73 at a still lower speed. Theairflow absorbs the heat from the coolant in an efficient manner in thesame manner as described above. The flow speed of the coolant can beadjusted depending on the number of the flat spaces 63, 68, 73 in theheat exchangers 31, 31 a, 31 b. In addition, the airflow runs across thegaps. This results in a further enhanced efficiency of heat radiation ascompared with the aforementioned heat exchangers 31, 31 a.

As shown in FIG. 12, the liquid cooling unit 27 may include a heatexchanger 31 c in place of the aforementioned heat exchangers 31, 31 a,31 b. The first and second flat plates 61, 62 of the aforementioned heatexchanger 31 are divided to extend in parallel with each other in thedirection of the coolant flow in the heat exchanger 31 c. Specifically,the heat exchanger 31 c includes a first flat plate 74 extending along areference plane, and a second flat plate 75 opposed to the front surfaceof the first flat plate 74. A flat space 76 is defined between the firstand second flat plates 74, 75. The flat space 76 serves as a flowpassage. The first and second flat plates 74, 75 are made of a metallicmaterial having thermal conductivity, such as aluminum, for example.

Likewise, the heat exchanger 31 c includes a third flat plate 77 and afourth flat plate 78 opposed to the front surface of the third flatplate 77. The third flat plate 77 is designed to extend along theaforementioned reference plane. A flat space 79 is defined between thethird and fourth flat plates 77, 78. The flat space 79 serves as a flowpassage. The flat space 79 is designed to extend in parallel with theflat space 76. In this case, the length L1 of the flat space 76 definedin the direction of the airflow from the ventilation opening 59 to theair outlet 33 may be set equal to the length L2 of the flat space 79likewise defined. The third and fourth flat plates 77, 78 are made of ametallic material having thermal conductivity, such as aluminum, forexample.

As shown in FIG. 13, the liquid cooling unit 27 may utilize a heatexchanger 31 d in place of the heat exchanger 31 c. The lengths L1, L2of the flat spaces 76, 79 of the aforementioned heat exchanger 31 c arechanged in the heat exchanger 31 d. Here, the length L2 of the flatspace 79 may be set larger than the length L1 of the flat space 76.Alternatively, the length L2 of the flat space 79 may be set smallerthan the length L1 of the flat space 76.

FIG. 14 schematically illustrates the inner structure of a notebookpersonal computer 11 a as a specific example of an electronic componentaccording to a second embodiment of the present invention. The notebookpersonal computer 11 a includes a liquid cooling unit 27 a placed in theinner space of the main body enclosure 12. The liquid cooling unit 27 aincludes a first heat receiver 81, a second heat receiver 82 and a heatexchanger 83 in place of the aforementioned first heat receiver 28,second heat receiver 29 and heat exchanger 31. A closed circulating loopis established in the liquid cooling unit 27 a. The first heat receiver81 is inserted in the closed circulating loop. Like reference numeralsare attached to the structure or components equivalent to those of theaforementioned notebook personal computer 11.

The fan unit 32 of the liquid cooling unit 27 a is placed outside theclosed circulating loop. The tank 37 and the pump 38 are placed outsidethe periphery of the printed wiring board 19. The tank 37 is placedbetween the printed wiring board 19 and the DVD drive 23. The pump 38 isplaced between the printed wiring board 19 and the hard disk drive 24.Screws may be utilized to fix the tank 37 and the pump 38 onto thebottom plate of the base 12 a, for example. It should be noted that anopening, not shown, may be formed in the bottom plate of the base 12 a,for example. In this case, the tank 37 and the pump 38 can be replacedthrough the opening of the bottom plate.

A partition plate 84 is placed in a space between the printed wiringboard 19 and the tank 37 as well as between the printed wiring board 19and the pump 38. The partition plate 84 may stand upright from thebottom plate of the base 12 a. The partition plate 84 serves to isolatea space containing the printed wiring board 19 from a space containingboth the tank 37 and the pump 38. Movement of air is thus preventedbetween the space for the printed wiring board 19 and the space for boththe tank 37 and the pump 38. The space for the tank 37 and the pump 38can be prevented from receiving airflow that has absorbed heat from thefirst and second LSI packages 21, 22 in the space for the printed wiringboard 19. The tank 37 and the pump 38 is thus prevented from a rise inthe temperature. The coolant is prevented from evaporation in the pump38.

As shown in FIG. 15, first and second air inlets 85, 86 are defined inthe bottom plate of the base 12 a. Fresh air is introduced into theinner space of the main body enclosure 12 from the outside through thefirst and second air inlets 85, 86. Here, the first air inlet 85 isopposed to the tank 37 in the inner space of the main body enclosure 12.The second air inlet 86 is opposed to the pump 38 in the inner space ofthe main body enclosure 12. The tank 37 and the pump 38 can be exposedto the fresh air outside the main body enclosure 12 in this manner. Thefirst and second air inlets 85, 86 may be combined with each other inthe bottom plate of the base 12 a.

Pads 87 are formed on the four corners of the bottom surface of the mainbody enclosure 12. The pads 87 protrude from the bottom surface of themain body enclosure 12. The pads 87 may be made of an elastic resinmaterial, such as rubber, for example. When the notebook personalcomputer 11 a is placed on the desk, the main body enclosure 12 isreceived on the surface of the desk at the pads 87. The pads 87 serve toestablish a gap between the bottom surface of the main body enclosure 12and the surface of the desk. The first and second air inlets 85, 86 arethus prevented from being closed with the surface of the desk.

As shown in FIG. 16, the inflow nozzles 47, 47 and the outflow nozzle 48are opposed to each other in the first heat receiver 81. The flowpassage 46 thus extends straight from the inflow nozzles 47, 47 to theoutflow nozzle 48 on the thermal conductive plate 45. As shown in FIG.17, the inflow nozzles 47 are designed to extend into the space 54 a.The outflow nozzle 48 is likewise designed to extend into the space 54.The inflow nozzles 47 and the outflow nozzle 48 are connected to theflow passage 46 at positions outside the periphery of the first LSIpackage 21 in the same manner as described above. This results inprevention of increase in the thickness of the casing 44.

As shown in FIG. 18, the heat exchanger 83 defines the flat spaces 76,79 extending along parallel lines in the same manner as theaforementioned heat exchanger 31 c. A pair of parallel metallic tubes 42is connected to one end of the heat exchanger 83. The coolant thus flowsinto one end of the flat space 79 through one of the metallic tubes 42.The coolant flows across the flat space 79 to one end of the flat space76. The coolant flows into the other metallic tube 42 from the other endof the flat space 76. The coolant is allowed to contact with the firstand second flat plates 74, 75 and the third and fourth flat plates 76,77 for a longer time in this manner. Simultaneously, the flow passage isnarrowed. The coolant is allowed to flow through the flow passagewithout stagnating. The airflow can absorb the heat of the coolant in anefficient manner.

When the flat spaces 76, 69 are defined to extend along parallel linesin the aforementioned manner, the heat exchanger 83 enables an intensivelocation of the metallic tubes 42, 42 at one end of the heat exchanger83. No metallic tube 42 needs to be connected to the other end of theheat exchanger 83. This results in reduction in the size of the heatexchanger 83. In addition, the positions of the metallic tubes 42 can bechanged depending on the positions of electronic components on theprinted wiring board 19. The heat exchanger 83 contributes torealization of wide possibility for arrangement of electronic componentsin the inner space of the main body enclosure 12.

The pump 38 allows circulation of the coolant through the closedcirculating loop in the notebook personal computer 11 a in the samemanner as the aforementioned notebook personal computer 11. Heat of theCPU chip 51 is transferred to the first heat receiver 81. Heat of thevideo chip is transferred to the second heat receiver 82. Thetemperature of the coolant thus rises. The coolant flows into the heatexchanger 83 from the second heat receiver 82. The heat of the coolantis radiated into the air through the heat exchanger 83. The coolant thusgets cooled. The airflow is discharged out of the main body enclosure 12through the air outlet 33. The cooled coolant flows into the tank 37.

The heat of the CPU chip 51 and the video chip is also transferred tothe printed wiring board 19. The heat spreads over the printed wiringboard 19 through wiring patterns on the printed wiring board 19. Sincethe tank 37 and the pump 38 are placed outside the periphery of theprinted wiring board 19, the tank 37 and the pump 38 are reliablyprevented from receiving the heat from the printed wiring board 19. Thisresults in prevention of rise in the temperature of the coolant in thetank 37 and the pump 38. The tank 37 and the pump 38 contribute toradiation of heat from the coolant into the inner space of the main bodyenclosure 12.

In addition, the tank 37 and the pump 38 are opposed to the first airinlet 85 and the second air inlet 86, respectively. Fresh air isintroduced into the main body enclosure 12 through the first and secondair inlets 85, 86. The tank 37 and the pump 38 are exposed to the freshair. The heat of the coolant in the tank 37 and the pump 38 can beradiated into the fresh air from the tank 37 and the pump 38. The heatof the coolant can be radiated into the air not only at the heatexchanger 83 but also at the tank 37 and the pump 38. The coolant getscooled in a highly efficient manner.

As shown in FIG. 19, the lengths L1, L2 of the flat spaces 76, 79 may bechanged in the heat exchanger 83 in the same manner as in the heatexchanger 31 d. In this case, the length L2 of the flat space 79 is setlarger than the length L1 of the flat space 76. Alternatively, thelength L2 of the flat space 79 may be set smaller than the length L1 ofthe flat space 76.

The liquid cooling units 27, 27 a can be incorporated in electronicapparatuses other than the notebook personal computers 11, 11 a, such asa personal digital assistant (PDA), a desktop personal computer, aserver computer, and the like.

1. An electronic apparatus comprising: a thin main body enclosure; adisplay enclosure pivotally coupled to the thin main body enclosure; aprinted wiring board located inside the thin main body enclosure, theprinted wiring board extending along a bottom plate of the thin mainbody enclosure; an electronic component mounted on the printed wiringboard; a closed circulating loop; a heat receiver inserted in the closedcirculating loop, the heat receiver having a thermal conductive platereceived on the electronic component, the heat receiver defining a flowpassage on the thermal conductive plate; a heat exchanger inserted inthe closed circulating loop so as to absorb heat from coolant; and atank inserted in the closed circulating loop, the tank being received onthe bottom plate of the thin main body enclosure at a position outside acontour of the printed wiring board so as to collect air in the closedcirculating loop.
 2. The electronic apparatus according to claim 1,further comprising a pump inserted in the closed circulating loop at aposition outside the printed wiring board so as to circulate the coolantalong the closed circulating loop.
 3. The electronic apparatus accordingto claim 1, further comprising a partition plate placed in a spacebetween the tank and the printed wiring board.
 4. The electronicapparatus according to claim 1, further comprising a keyboard embeddedin a surface of a cover of the thin main body enclosure.
 5. Theelectronic apparatus according to claim 1, further comprising: an airinlet defined in the bottom plate of the thin main body enclosure at aposition opposed to the tank; and a fan unit mounted on the printedwiring board so as to generate airflow directed to the heat exchanger.6. The electronic apparatus according to claim 1, wherein the displayenclosure is coupled to a rear end of the thin main body enclosure, thetank includes a coolant outlet at an end farthest from the rear end ofthe thin main body enclosure, the tank being elongated toward the rearend of the thin main body enclosure from the end farthest from the rearend.
 7. An electronic apparatus comprising: a thin main body enclosure;a display enclosure pivotally coupled to the thin main body enclosure; aprinted wiring board located inside the thin main body enclosure, theprinted wiring board extending along a bottom plate of the thin mainbody enclosure; an electronic component mounted on the printed wiringboard; a closed circulating loop; a heat receiver inserted in the closedcirculating loop, the heat receiver having a thermal conductive platereceived on the electronic component, the heat receiver defining a flowpassage on the thermal conductive plate; a heat exchanger inserted inthe closed circulating loop so as to absorb heat from coolant; and apump inserted in the closed circulating loop, the pump being received onthe bottom plate of the thin main body enclosure at a position outside acontour of the printed wiring board so as to circulate the coolant alongthe closed circulating loop.
 8. The electronic apparatus according toclaim 7, further comprising a partition plate placed in a space betweenthe pump and the printed wiring board.
 9. The electronic apparatusaccording to claim 7, further comprising a keyboard embedded in asurface of a cover of the thin main body enclosure.
 10. The electronicapparatus according to claim 7, further comprising: an air inlet definedin the bottom plate of the thin main body enclosure at a positionopposed to the pump; and a fan unit mounted on the printed wiring boardso as to generate airflow directed to the heat exchanger.